Wide strip cold rolling



Nov.-16, 1937. 1.. s. DAHL ET AL 2,099,261

WIDE STRIP COLD ROLLING Filed July 19, 1954 2 Sheets-Sheet l Fig.1.

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LHWEENCE 5. Der/#4 and JOHN H. SHLLTZ.

Nov. 16, 1937. L. s. DAHL ET AL 2,099,261

WI-DE STRIP COLD ROLLING Filed July 19, 1934 2 Sheets-Sheet 2 Patented Nov. 16, 1937 WIDE STRIP COLD ROLLING Lawrence S. Dahl and John H. Shultz, Gary, Incl, assignors to American Sheet and Tin Plate Company, a corporation of New Jersey Application July 19, 1934, Serial No. 736,128

3 Claims.

Our invention is a method and apparatus for rolling strip metal, and more specifically pertains to a method.v of operating cold rolling mills so as to obtain a more uniform and specific thickness of such'strip metals.

Such mills for the thickness reduction of long continuous strip metal may be of the two, three, four high or of the Cluster type, either as set up in a non-reversible series or tandem or as a single reversible stand. Coiling means are provided on one or both sides depending on whether the set-up is tandem or single. For illustrative purposes only we hereinafter confine the .disclosure of our method and apparatus to a single four high reversing mill wherein coiling means are located on either side of said mill for alternately receiving and feeding the strip.

Heretofore it was generally understood and believed that maintenance of constant tension on the strip between the coiling reels and the mill was all that wasnecessary in order to properly guide and feed the material into and through the mill and to obtain flat delivery of the strip to the reels. The proper gage or thickness of the strip was obtained entirely by variation of screw pressures exerted against the material being rolled through predetermined spaced rolls.

This manner of rolling is satisfactory to a certain degree where slight gage variations are permissible. It does not, however, take into consideration any variable factors of the strip such as off-gage from hot rolling, variation of chemical composition, work hardening capacity or physical properties all of which would further aggravate the non-uniformity of gage irrespective of the roll pressures applied.

With the advent of the single stand reversing mill higher operating speeds of metal movement have necessitated that means. be provided for taking care of the above mentioned variables if uniform gage is desired. Any attempt to correct such internal or external variations of the strip by changing screw pressures is costly and undesired, for with the higher operating speeds a few seconds delay awaiting a screw change Produces many lineal feet of undesirable nonuniformly gaged strip.

Furthermore, with such increased speed of operation together with the producing of light gage finished strip, it is extremely advantageous to produce not only a uniform gage but attain this uniformity in conjunction with the specific gage. This is accomplished, according to our invention, by varying the tensional effect on the strip on the delivery side of the mill, ii dc sired, also by varying the tensional eflect on the entry side. This method, in conjunction with the manipulation of the pressure screws, oii'ers a simple, rapid and satisfactory arrangement for obtaining the much desired specific as well as uniform gage.

The prime object of this invention, therefore, is to provide adequate methods and means for producing at one and the same time both uniform and specific gage in strip metal as rolled at relatively high speeds and into thin gages.

In the drawings:

Figure 1 is a top plan of a rolling mill.

Figure 2 is a side elevation.

Figure 3 isa wiring diagram.

Only one continuous cold rolling strip mill of the conventional type is illustrated. It includes a reversing 4-high stand of pressure working rolls I supported in the usual manner and driven by a motor 2. Reels 3 are'mounted on both sides of the stand to carry relatively wide metal strip in coils for reverse passage th'erethrough. Each of the reels 3 is provided with a driving motor 4 which powers it when receiving and coiling strip. The reels are also generally provided with some sort of a drag which is coupled to whichever coil is discharging to apply a restraint to the leaving strip. No illustration of such drags is attempted as the motors 4 may be used by operating them as generators, or other well known expedients resorted to.

Ordinarily this type of mill is operated so that the pressure screws 5 exert a pressure on the rolls I, which roll pressure aids the metal tobe rolled to gage. This is done by a number of reversing passes. In some mills the reduction is effected by the speeding up of the motors 4 so that the strip is pulled through the rolls I, the latter being idly run. Some mills of this type have, as illustrated, the work contacting rolls as well as the reels driven. In all cases the gage of the strip is attained entirely by the setting of the rolls l by the pressure screws 5. When the mill is operated in either manner a tensional effect also results, but the gage is regulated only by the roll setting and screw pressures, and in no other manner.

According to the present invention, the strip may be given a number of reversing passes through the rolls I until the required gage is almost attained. No effort is necessarily made to control the torque and speed of the motors 4 during these passes beyond that required to assure a tight coiling and to produce a fiat strip.

When the correct gage is almost attainedthe pressure working rolls i are set to secure a very close approximation of the required gage, care being taken, however, that any possible variations are slightly over instead of under this gage. Mills of the .character under discussion almost always include remote indicating electrically operated gages 6 for the purpose of judging the works size of thickness, and it is with the aid of these that the above results are attained.

With the working rolls I set in the above manner the strip is then given one or more finishing passes. Exact gage of the strip for its entire length is attained and uniformly held by varying the power input and torque of the motors 4 so that the strip material is stressed beyond the elastic limit but below the ultimate strength, and tensionally reduced as required. This is believed novel, and provides an easy method of operating existing mills' to produce a superior product.

A slight alteration of the above procedure consists in operating the motors 4 during these finishing passes with a power input and at a speed which continuously yet variably applies reducing tensional strains to the strip both exiting from as well as entering the rolls. This not only enables the correction of oversize strip but will also control undersize variations, inasmuch as this reduction is calculated to bring the strip to size when added to the rolling effect of the rolls.

The entire reduction in gage due to screw pressure on the rolls and variable tension on the strip takes place within and immediately adjacent the rolling arc or contact area of the rolls and the strip material, the control of such accuracy of gage being manifested on the delivery side.

Therefore, briefly stated, the invention consists in either setting the working rolls of a mill to produce as exact a gaged product as possible with any existing variations oversized being corrected by variable tensional reductions or, as an alernative, the deliberate setting of these rolls to produce relatively oversized strip, and the reduction of this strip by tensions which are varied as required to control the gage. This variation of tension on the strip is thus obtained by increasing or decreasing the power input to the motors 4 and accordingly varying the torque applied to the reels.

The only alterations of the mill necessary consist in the insertion of a Vernier rheostat I in series with the regular rheostat 8 which normally controls the power input to the motor 4. This Vernier rheostat then provides for fine motor adjustment by giving a plurality of amperage variations in steps which are much smaller than may be attained by the regular rheostat 8.

in carrying out this method a roller stands with his hand on the control lever of the Vernier rheostat I and watches a remote gage operated by one or the other of the flying micrometers 6, and by operating the rheostat I varies the power input and consequently the torque and/or speed of either or both motors 4, as required.

The increase or decrease in the power input to either of the motors 4 imposes a proportional increase or decrease in the torque applied to the strip by the reels 3, due to the tendency to vary the speed of rotation of the reels 3. It will be understood, however, that the increase or decrease in the speed of the reels 3 may or may not be proportional to the tensional eifect resulting from the torque applied to the strip being rolled. Therefore, while the speed of the reels 3 varies with the variations in power input to the motors 4, such speed variations may not be in direct aoeaaei proportions to the variations in power input, and the torque or power input is the governing factor for obtaining the desired tensional effects.

In mills of the characterdescribed it is impossible to quickly adjust the pressure of the working rolls I, because the mass of their screws 5 is too great to be so handled. The roller must ordinarily, therefore, depend almost entirely upon the initial setting of these rolls to secure results, and cannot quickly compensate for variations in the strips mechanical or chemical structure, and this naturally results in gages which are not uniform.

To compensate for these variations, in addition to producing uniform flatness and the specified gage, the operator makes rapid changes in the power input and speeds of either or both motors 4 by manipulation of the Vernier rheostat 1 in accordance with the showing of the recording gages 6. This produces rapid changes in either or both the back or pull tensions as exerted by the motors 4 acting on the delivery or take-up reels, respectively. These opposite torques brought about by opposite reels set up a tensional pull on the strip at or immediately adjacent the contact arc of the rolls and strip material in a manner which gives to the applied roll pressure that increment which permits accurate control of desired gage. The work rolls may or may not be driven, as both are predeterminedly set to the approximate gage thickness desired, and the variable tensional effect may be used to the same advantage in either case. This means that the correction of gage is practically instantaneous, thus avoiding the loss of many feet of ofi-gage strip, especially in mills traveling at high speeds, a loss which would be necessary if waiting for screw pressure adjustments.

While we have shown and described one specific embodiment of our invention we do not wish to be confined thereto, since various modifications may be made, such as tandem or single mills, reversing or non-reversing, and of the two, three or four high as well as Cluster type, without departing from the scope of our invention, as defined in the following claims.

We claim:

1. A method of cold working metal strip to a thinner predetermined gage, including working said strip primarily by pressure rolling to a thickness slightly greater than said gage, then applying suflicient tension to said strip to effect drawing and varying said tension as required to draw said strip to said gage, said tension being at all times suficient to effect at least some drawing.

2. A method of operating a metal strip cold rolling mill of the type providing at least one stand of pressure rolls, a reel for coiling strip leaving said rolls and means for applying varying torques to said reel, said method including finishing metal strip passing through said rolls and coiling on said reel to the desired gage by maintaining a constant roll pressure throughout the passage of said strip, regulating said means to apply a torque to said reel such as will continuously tension said strip beyond its elastic limit at all times during its passage through said rolls to said reel, and varying said means to cause it to apply lesser or greater torques to said reel as required to tension said strip to draw it uniformly to sa'id desired gage throughout at least a majority of its len th.

3. A method of operating a metal strip cold rolling mill of the type providing at least one stand of pressure rolls, a reel for coiling strip leaving. said rolls and means for applying varying torques to said reel, said method including working metal strip passing through said rolls and coiling on said reel primarily by pressure rolling until a thickness at least slightly greater than the ultimate gage desired is attained, and

then finishing said strip by maintaining a constant roll pressure, regulating said means to apply a torque to said reel such as will continuously tension said strip beyond its elastic limit and varying said means to cause it to'apply lesser or greater torques to said reel as required to tension said strip to draw it uniformly to said ultimate gage throughout at least a majority of its length, said varying of said means being regulated so that the latter always applies a torque to said reel such as will tension said strip at least slightly beyond its elastic limit;

, LAWRENCE S. DAHL.

JOHN H. SHULTZ. 

